Advancements in technology have led to smaller and more compact microelectronic devices. The result is an increasing need in the microelectronic field for very dense microelectronics systems. To reduce the size of the electronic device, the area required for the integrated circuits comprising the device must also be reduced. Thin film structures were designed to solve this problem. In a thin film structure an interconnect is fabricated on a substrate using alternating layers of insulating and conductive material. Typical interconnects are constructed of polyimide layers and copper layers. Additional electrical components can be attached to the interconnect. By using an extremely thin substrate, the size of the integrated circuit can be decreased even further. This construction is known as a “flex circuit.”
“Flip-chip” technology is frequently used to manufacture flex circuits. Flip-chip technology consists of turning the semiconductor integrated circuit, or chip, upside down during processing to connect the integrated circuit to the substrate. In this process the circuit side of the integrated circuit is generally bonded to the substrate using solder. The alignment of the chips to the substrate must be fairly precise during attachment. However, the flexible nature of thin substrates makes it difficult to achieve the necessary precision during attachment and presents a significant problem during fabrication of flex circuits. Prior art methods have attempted to solve the problems associated with integrated circuit alignment through mechanical fixtures or laser drilled holes to assist in alignment. However, these methods require extra tooling at significant expense and also cause damage to the underlying device. Therefore, rigid substrates have been chosen for many applications where a thin substrate would be more desirable.
U.S. Pat. No. 5,998,291, entitled “ATTACHMENT METHOD FOR ASSEMBLY OF HIGH DENSITY MULTIPLE INTERCONNECT STRUCTURES,” discloses a method for fabricating a high density multiple interconnect decal using multiple substrates. The flexible interconnect is first secured to a substrates and a protective film is applied to the interconnect. A carrier is secured to the protective film to create a flat surface on the interconnect. The module is then secured to a mounting substrate. The carrier and protective film are thereafter removed, leaving only the interconnect and the mounting substrate. The electrical components are mounted on the interconnect at this point. The present invention does not process semiconductors in this manner. U.S. Pat. No. 5,998,291 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,183,588, entitled “PROCESS FOR TRANSFERRING A THIN-FILM STRUCTURE TO A SUBSTRATE,” discloses a method for manufacturing a semiconductor device structure consisting of at least a thin film structure and a metal interconnect. A dielectric layer is deposited on a primary carrier. The metal interconnect is deposited on the dielectric layer and the thin film structure is built on the metal interconnect. A release interface is defined between the dielectric layer and the metal interconnect to facilitate release of the thin film structure and metal interconnect from the primary carrier. In an alternative embodiment, the thin film structure is attached to a permanent substrate prior to release of the primary carrier. The present invention does not use this method to process thin film structures. U.S. Pat No. 6,183,588 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,194,245, entitled “METHOD FOR MAKING THIN FILM SEMICONDUCTORS,” discloses a method for epitaxially growing a semiconductor thin film on a semiconductor substrate. The semiconductor substrate includes a porous structure allows the semiconductor thin film to be easily separated from the substrate after fabrication of the semiconductor thin film, which is a preferred embodiment is a flexible thin film. In another preferred embodiment, a transparent substrate is attached to the top surface of the semiconductor thin film prior to separation of the semiconductor thin film from the semiconductor substrate. The present invention does not process semiconductors in this manner. U.S. Pat. No. 6,194,245 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 5,499,444, entitled “METHOD OF MANUFACTURING A RIGID FLEX PRINTED CIRCUIT BOARD,” discloses a method of manufacturing a circuit board from a flex layer using a hot press operation. To achieve this, windows are drilled through the flex layer and each other circuit layer, the windows are aligned, and protrusions from the press are inserted through the windows to align the structures during fabrication of the final product. The present invention does not use this method of circuit fabrication. U.S. Pat. No. 5,499,444 is hereby incorporated by reference into the specification of the present invention.
As can be seen from the prior art, one difficulty with production of a flex circuit is that several support structures must typically be used to create the flex circuit. After creation of the flex circuit, alignment structures are then used to allow electronic devices to be attached to the substrates. These additional alignment structures frequently require alteration of the circuit, add significant additional production expense, and do not provide the precision necessary for the alignment operation. It is therefore desirable in the art to have a method for producing a flex circuit and aligning it with electronic components without the use of multiple external devices.